Nationally, a MORI survey showed that 92 per cent of parents of assisted place holders earn less than #163;25,000 a year, and the number who are unskilled workers or unemployed has risen in six years from 16 per cent to 28 per cent.
Judith Sischy, director of the Scottish Council of Independent Schools, says: "Labour politicians make sweeping statements about the independent sector but very few have ever been in one of our schools. They simply quote perceptions which are out of date and misinformed. I would like to take them by the hand and walk them through the schools. Labour does not seem to know that parents who send their children to independent schools are ordinary folk. Who do they think these people are?"
Mrs Sischy dismisses as without substance the claim by Helen Liddell, Labour's education spokeswoman, that some self-emplo yed people use accounting loopholes to abuse the scheme.
She adds: "I have a massive problem with Labour's attitude that you cannot be a true Labour supporter if you send your child to an independent school and take an assisted place. It is an infuriating attitude and quite false."
Having identified ages three to seven as the "golden years", Labour has pledged to cut class sizes to a maximum of 30 by phasing out assisted places. On the party's figures, this would release at least #163;20 million a year across Britain and enable the pledge to be met within three years.
But the Institute of Public Finance puts the cost at #163;65 million annually with an estimated #163;100 million in capital costs. Savings from phasing out the scheme would amount to no more than #163;49 million annually after taking into account the cost of educating extra pupils in state schools.
The average state secondary place in Scotland costs #163;2,800, without including spending on buildings, capital costs and central services. Assisted place pupils are an average charge on the public purse of #163;3,600 a year. Labour says #163;1.8 million a year will be saved in Scotland,but the independents claim that far greater savings are available by cutting the state sector's 300,000 surplus places. More than half of these are in Glasgow.
Only 4 per cent of Scottish children are educated at independent schools, 31,000 in all. Around 20 per cent of Edinburgh children go private while in Perth and Kinross, Aberdeen and Glasgow the figures are 12 per cent, 9 per cent and 8 per cent respectively.
Mrs Sischy says: "If Labour were to freeze the assisted places grant it would be a false promise on their part that children already in assisted places can finish their education in an independent school because the value of the grant would not be maintained. If assisted places are phased out without great care there will be chaos, and it will be very cruel indeed if it is done quickly." She adds: "We welcome greater sharing of facilities with state schools but assisted places is the main obstacle in talking about partnership."
But talking with whom? There is a tacit admission that while the independent sector has kept in close touch with national politicians, relationships with local authorities have been neglected. The plan now is to win hearts and minds wherever councillors are prepared to listen.
Keith Pearson, soon to retire as headteacher of George Heriot's in Edinburgh, says: "Education should not be a political football. I deplore the fact that a change of political party can damage the income of a school. For a school like ours assisted places have been a boon, have helped us to continue our ethos. There is bound to be a change in that if the system goes."